Method of rolling magnetic material



June 22, 1937. N R 2,084,337

METHOD OF ROLLING MAGNETIC MATERIAL F iled Dec. 1, 1954 lNGoT HEATED ROLLEDINTO SLABs -To ABOUT 2 00 E oRABpv FINISHED AT TEMPERATURE (AB UT I900 F.

OR BELow) J0 DETERMINEb BY NATIURAL COOLING Ro LEo INTO STRIP & COILED To h? ZQB'EP'F J3 i a Q C) 8 J? 0 0 RoLLme o CONTROLLED AS TO Fl ISH AT ABOUT |450E STmP COLD ROLLED TO FINISHIED GAuss INVENTOR Patented June 22, 1937 UNITED STATES PATENT OFFICE- METHOD OF ROLLING MAGNETIC MATERIAL sylvania Application December 1, 1934, Serial- No. 755,515

3 Claims.

My invention relates to the making of magnetic material and, in particular, to the manufacture, of such material in the form of thin sheets or laminations adapted for the assembly 5 of cores of electrical apparatus of various types.

This application is in part a continuation of my copending application Serial No. 718,789, filed April 3, 1934, for Metal rolling.

So-called electrical sheets have generally been made heretofore by hand on a two-high hot mill. In my Patent No. 1,965,559, I have disclosed a method of producing a highly superior grade of magnetic material by cold rolling and heat treating hot rolled strip. I have discovered that the quality and characteristics of the final product, particularly its permeability at high fiux densities, and hysteresis and eddy current losses, are determined not only by the procedure followed in reducing the hot strip to final gauge,

0 but also by the processing -of the slabs from which the hot strip is rolled and, furthermore, the manufacture of the slabs from the ingots. While the invention has particular reference to silicon steel containing about 3% or less of silicon, it is not limited thereto and may be utilized in the manufacture of any magnetic materlal, regardless of composition.

For a complete understanding of the invention, reference is. made to the accompanying drawing illustrating the invention diagrammatically and the appended description relating thereto. In the drawing:

Figure 1 is a diagram illustrating the manufacture of slabs from the ingot;

Figure 2 is a diagram illustrating the manufacture of strip from the slabs; and

Figure 3 is a diagram illustrating the manufacture of the finished product from the hot strip.

40 In accordance with my invention, I prepare a melt of silicon'steel containing 3% silicon or less, and pour it into ingots of any convenient size. After solidification, the ingots are heated to a temperature of about 2000 F. or above.

They are then ready to be rolled into slabs. This stage of the operations is shown diagrammat-' ically in Figure 1 of the drawing.

The ingot Ill may be reduced to slab form by any convenient means, rolling, forging, or otherwise, but I preferably subject the ingot to rolling in a suitable rolling mill and shear the resulting product into slabs I2. I preferably complete the rolling of the ingot into slabs at one heat, the slabs being finished while at a temperature 56 of 1900 F. or below, determined by the naturalcooling of the ingot as it is rolled down into slab form.

The slabs 12' thus produced are reheated to a temperature of about 2000 F. or above. They are then ready for reduction to strip form, shown at l3, which may best be accomplished by rolling, either in a continuous mill H or in a reversing mill, both of whichare well known. For convenience, the material is preferably coiled during the later stages of the reduction into strip and, in any case, after the final reduction. This stage of the operations is indicated diagrammatically in Figure 2.

Therolling of the slab into strip form seems to exercise an effect upon the final results obtained as great as that of the rolling of the ingots. I have found that the greatly improved results are produced by heating the slab to a temperature of between about 2000 and 2100 F. for a period of time sufiicient to permit thorough penetration of the heat into all parts of the slab uniformly, the time depending somewhat on the silicon content, and the nature of the practice followed in casting and finishing the ingot. For a 3% silicon steel, I prefer to heat the slabs to a temperature between about 2000 and 2050 and hold themat that temperature until the slab is thoroughly heated throughout, to the same temperature in all parts.

After heating to a temperature in the vicinit} of 20002l00 F. for the time specified, which heating may be conducted in a. convenient manner in any desired type of furnace, I remove the slabs from the heating zone and permit them to cool to a temperature such that when they have been rolled to final gauge, the temperature has decreased to a value sufficiently below the temperature of the first heat treatment. to which the finished strip is subjected (usually about 1600 F.) to insure quick response to recrystallization on such subsequent heating. I prefer to finish the hot strip at 1450 F. or below, although good results may be obtained even if the strip is finished at a temperature as high as 1500 F. or 1550 F. Usually, it is highly desirable to permit the slabs to cool from their initial temperature to about 1900 before the rolling is started. In the ordinary continuous mill, the temperature will have been reduced from that figure to about 1450 by the time the rolling has been completed. It is possible to finish at a lower temperature, say 1200" or 1300 F. with equally satisfactory results, the prime consideration being to finish at a temperature not much higher than 1450". This finish- 1450" F. or below.

i'iiflgtstemperature to produce the best re- Theheating oi theslabsinitiallytoa temperature oiiabout 2050 Elappears to be highly important. It has been found that'i! the slabs are initially heated to alhigher temperature, say 2300". or'2200 l". andthen ilnished, the results are not so good as to 2050,- even though the Likewise, heating theorist initially to about moo -1900" or less and rolling so that the strip is finished at 1450? or below, produces results which are not so good as those 0! the'preierred method. The results obtained with a variety oi practices difl'ering slightly irom the preierred method indicate the desirability oi the latter as compared to any variant thereoi.

The importanceoiflnishingthestripat 1450 F.orbelowisdemonstratedbytheiactthatin one mill, where it wash to roll the slab immediately'onleaving the furnace due to the set-up of the mill, the strip was'flnished between 1550" and 1600but the product was very inferior magnetically to'that produced by the preferred method. I I g The initial heating-oi the ingot to a temperature of 2000 F., or above, is also of great importance. If the ingot is heated to only 1800' 11"., ior example, and the resulting billets p i in accordance with the preierred practice outlined herein, the final product will not have characteristics as desirable as ii the ingots were initially heated to 2000 orv above before bein iormed into slabs;

Aiter the hot strip has been rolled, coiled and cooled, it is ready for reduction in thecold to final gauge, in accordance with the disclosure oimy above mentioned Patent No. 1,965,559. 'lhis stage oi the operation is indicated diagrammatically in Figure 3; showing a iour-high reversing mill IS with winding and unwinding reels l6.

To generalize from the results at much experiment, I may say that, inaddition to .the method for reducing the hot strip in the cold to final gauge, disclosed in my patent aforementioned, the development oi the most desirable quality in theflnalproduct appears to require the initial heating oi both the ingot and slabs to a relatively high temperature, say 2000 1".

or above, beiore reducing them respectively to slabs andstrlp, and the finishing oi thehot rolled strip at a relatively much lower tempera ture, in theneighborhood'oi 1450 F. I

Iamawarethatithasbeenhereto-.

slabsareheatedonly; strip is iinishedi at' ioretoheatsiliconsteelcontainingupwardsoi 5% IUIOOILUOIWWIBMBPPT" 2000' ior the'purpose at increasing the ductility.

" temperature oi around 1400 I. It has not, however, been possible by such methods to obtain the desirable results flowing irom my meth- 'od; including theinitial heating oi the slab to a relatively high temperature, as well as the finishingoi the hot rolling oi the strip at a relaively much lower temperature.

WhileIhave describedherein but one preierred practice oi the method oi my invention. it will be apparent. that certain changes therein may be made without departing irom the spirit oi the invention or scope oi the appended claims.-

For example," instead oi, subjecting the slab to aspecial cooling operation to insure' that the strip will be-flnished at a temperature oi 1450 F. or below, I may control'the rate oi rolling or the rate oi cooling whfle rolling so ssito produce the desired temperature in .finishing, without any special intermediate cooling'step.

I claim: i. In a method oi making magnetic material having improvedmagnetic properties, the steps including heating an ingot oi silicon-iron alloy containing about 3%, silicon to a temperature 'ot-the material. I do not'believe thatit has ever been proposed heretofore to improve the magnetic qualities oi magnetic material by heating it to such temperatures in the ingot term,

above 2000 F., reducing the ingot to slab 'iorm without reheating it, and reducing the slab to. strip aiter heating the slab to-about 2000 F.,

finishing at 1450 F. or

2. A method oi making magnetic material the steps including heating an ingot oi slliconsteel" containing about 3% silicon to a temperature oi about 2000 F., reducing the ingot to slabs. heating the slabs to about 2000 'F., reducing the slabs to strip andilnishing the strip rolling while the material is at a temperature oi about '3. In a method oi making. magnetic having improved properties, the steps including heating an ingot oi silicon-iron alloy containing about 3%silicon to a temperatm'e above 2000 I.

and rolling the ingot into strip, flnishing the rolling oi the strip when it is at a temperature oi 1450I'.o1'below.

Norman P. does. 1 

